Many occasions arise where it is desirable or necessary to dig trenches or channels or to remove material from the bottom of a lake, river, ocean or other body of water. For instance, a harbour or channel may require clearing to enable vessels to enter without grounding. Earth and other material may also have to be removed for laying pipe or placing an object in the bed of the body of water. Alternatively, an object buried or laying in the bed of a body of water may have to be removed which requires the excavation of the soil and bottom materials in which the object is imbedded without damaging the object.
Unless the area to be dredged is near to the shore of the body of water, the dredging apparatus must be operated from some kind of a work platform located on the surface of the water. A vessel floating on the body of water may be used to provide the work platform from which to perform the dredging operations.
Dredging may occur through the use of a mechanical shovel, bucket, or other scoop-like structure to remove the earth, rocks and other materials from the bottom of the body of water. These structures generally allow for little control over the actual dredging operation. As a result, there is little precision with respect to the channel being dug or the material being removed.
In addition, U.S. Pat. No. 3,171,219 issued Mar. 2, 1965 to C. P. Kaufmann et. al. and U.S. Pat. No. 3,218,739 issued Nov. 23, 1965 to C. P. Kaufmann et. al. disclose an underwater dredging apparatus which includes a water-tight submersible hull. Mounted at one end of the hull is a power driven rotary cutter. The cutter is designed to loosen the material on the bed of the body of water so that the material may be drawn into an intake pipe and expelled out of an outlet pipe away from the site being dredged. The cutter is capable of being raised and lowered vertically in the water and rotated about a substantially vertical axis. This dredging apparatus allows relatively greater control over the dredging operation than a shovel or scoop structure. However, the use of the cutter may damage an object being removed from the bottom surface and the movement of the cutter during the dredging operation is limited, resulting in a lack of precision with respect to the removal of bottom materials.
U.S. Pat. No. 4,932,144 issued Jun. 12, 1990 to N. V. Sills and U.S. Pat. No. 4,073,078 issued Feb. 14, 1978 to J. H. Leitz overcome some of the disadvantages of both a mechanical scoop and a cutter by utilizing a current of water to perform the dredging operation. The current or flow of water dislodges materials on the bed of the body of water. However, the movements of the dredging apparatuses disclosed in these patents are also limited during the dredging operation. As a result, there continues to be a lack of precision with respect to the removal of bottom materials. In particular, U.S. Pat. No. 4,932,144 to Sills is directed towards a dredging unit which is deployed remotely from a vessel. The unit is placed in position on the bed of a body of water and is kept in contact with the bottom surface throughout the dredging operation. As a result, the current of water performing the dredging can only be directed perpendicular to the bed. U.S. Pat. No. 4,073,078 to Leitz discloses an agitation propeller for producing an eroding current to perform the dredging operation. The agitation propeller is attached to an extendable and retractable elongate leg which is adjustable vertically beneath the work platform. Once lowered to the desired depth, the propeller can be rotated only about a substantially vertical axis. However, shrouds may be attached to the sides of the propeller to direct the eroding current in a predetermined desired direction, but the specific angle of the eroding current relative to the bed of the body of water cannot be controlled or varied during the dredging operation.
In addition, in order for the above described apparatuses to achieve some control over the dredging operation, U.S. Pat. No. 3,171,219 to Kaufmann, U.S. Pat. No. 3,218,739 to Kaufmann, and U.S. Pat. No. 4,073,078 to Leitz require the dredging apparatus to be affixed mounted or otherwise relatively permanently attached to the vessel or work platform structure from which the dredging operations are being performed. Thus to achieve even limited control of the dredging operation, the portability of the dredging apparatus is eliminated and the vessel or work platform requires specific structural alterations and adaptations to accommodate the use of the specific dredging apparatus.
Finally, the vessel or work platform from which the dredging operation is conducted typically has no independent means of propulsion. As a result, when a vessel is to be used as a platform for dredging operations, it must be pushed or towed to the work site by a powered vessel. To overcome the disadvantages associated with having no means of propulsion, U.S. Pat. No. 3,440,743 issued Apr. 29, 1969 to G. T. F. Divine mounted an underwater apparatus in the hull of a ship which may be utilized either for dredging or for propulsion of the ship to its desired location. However, in combining the dredging apparatus with a means of propulsion, the ship requires substantial alterations and adaptations which render the dredging apparatus completely non-portable. As well, the dredging apparatus and thus the dredging operation may be controlled in only a very limited fashion. For instance, the apparatus is not adjustable vertically and is therefore not able to be used in deeper waters. As well, the direction of the current of water produced for the dredging operation is controlled through sets of diverters which are set at a predetermined angle and cannot be adjusted during the dredging operation.
Although not dealing with dredging operations specifically, U.S. Pat. No. 3,076,425 issued Feb. 5, 1963 to J. C. Anderson, U.S. Pat. No. 3,211,124 issued Oct. 12, 1965 to P. J. Mantle, U.S. Pat. No. 3,332,388 issued Jul. 25, 1967 to A. L. Moraski, U.S. Pat. No. 1,484,109 issued Feb. 19, 1924 to W. F. Beatty, and U.S. Pat. No. 3,987,748 issued Oct. 26, 1976 to C. A. Carroll all deal with various forms of vessels or platform structures which are adapted to support and be powered by a land vehicle, namely an automobile. Operation of the automobile in the conventional manner both propels and steers the vessel through the water. In each of these patents, the vessel or platform is substantially altered or adapted to accommodate the automobile, and the propulsion and steering mechanisms are affixed or mounted to the vessel in such a manner that they form part of the vessel structure.
There is therefore a need in the industry for a dredging apparatus which allows for greater control over the dredging operation while it is being performed and greater precision with respect to the removal of bottom surface materials, as compared to existing dredging apparatuses. In addition, when the dredging operation is being performed away from the shore of the body of water, there is a need for the apparatus to be relatively portable for use on any available vessel or work platform structure, and for it to be capable of both propelling the vessel on the body of water and performing the dredging operation.